This study proposes to evaluate the hemacytometer leukocyte adherence inhibition assay for its utility in detecting and differentiating cancer in humans. An attempt will be made to quantify the assay. By use of quantitative differences, the value of the system will be estimated for its ability to predict the clinical course of cancer patients. The study is designed on the statistical basis of a 4-way (nested) analysis of variance. Elaborate precautions have been devised to assure a well-controlled, blind and unbiased study. The hemacytometer assay will be compared with the tube LAI assay and also the leukocyte migration inhibition assay for tumor immunity in humans. These may provide complementary information since they depend upon different principles from the hemacytometer system. Finally, a small study is contemplated in which the LAI system will be analyzed for its ability to reflect genetic restriction in the cell-mediated response to soluble tumor antigens or defined proteins in responsive human donors.